how big is the lump? it could be as simple as a pore clogged with oil. it can feel like a cyst and by massaging it you can get it to head over time. Or try a warm wash cloth.
Shot reactions, like they said, are on the shoulder blades. Caesar has a reaction to a shot and his shoulder blew up to a softball size. The vet tech that gave a shot didnt insert it in the correct manner and it dissolved with time and a Benadryl shot.
Does your pup react when you touch it like it might hurt?
What size is it?
When Cairo was being neutered the vet pulled two teeth (canine and molar) that were not completely out or pushed out by the new teeth. They didnt charge me that much because he was already asleep. This is a great time for them to inspect and fix anything. They charged me $50 for pulling a baby canine that didnt come out and a molar that was on its way out.